1. Field
The disclosed concept pertains generally to glowing contacts in power circuits and, more particularly, to methods of detecting such glowing contacts. The disclosed concept also pertains to apparatus for detecting glowing contacts in power circuits.
2. Background Information
Circuit interrupters include, for example, circuit breakers, receptacles, contactors, motor starters, motor controllers and other load controllers.
A glowing contact is a high resistance electrical connection, which can form, for example and without limitation, at the interface of a conductor (e.g., wire) and a screw terminal (e.g., line terminal; neutral terminal), for example, of a receptacle. A glowing contact is also possible, for example and without limitation, at a receptacle outlet where a male three-prong plug mates with three-sets of outlet contact blades of the receptacle outlet. A glowing contact at a receptacle is known to produce substantial heat that can melt the receptacle and start a fire. It is very easy to create a high resistance or glowing contact at a receptacle terminal using copper wire. The hazards associated with glowing contacts, including contacts made with all combinations of copper, brass and iron are known. See, for example, U.S. Pat. Nos. 6,948,846; and 6,707,652.
According to UL 1699 (Arc-Fault Circuit-Interrupters) (scope 1.3), arc fault circuit interrupters (AFCIs) providing arc fault detection are not intended to detect glowing connections and, thus, it is believed that AFCIs do not provide glowing contact protection.
Overheated electrical connections can result from loose connections in electrical components such as panelboards, load centers, electrical outlets and lighting switches. Frequently, these electrical connections go undetected, can lead to the destruction of the electrical component, and many times create a fire.
It is known to employ a temperature sensor (e.g., a thermal relay; a bimetal) to sense a temperature at about 200° C. and provide glowing contact protection for a receptacle.
U.S. Pat. No. 6,707,652 discloses a receptacle including a first temperature sensor that outputs a first signal representative of a first temperature of a line circuit, a second temperature sensor that outputs a second signal representative of a second temperature of a neutral circuit, and a circuit that provides a glowing contact trip signal as a function of a difference between the first temperature and the second temperature.
It is also known to detect glowing contacts or resulting overheated conditions by detecting smoke or gas emitted from overheated plastic, by employing active acoustic sensing to detect an electrical conductivity fault of a power circuit, or by other mechanisms to protect from overheating conditions.
There is room for improvement in methods of detecting glowing contacts in a power circuit.
There is room for improvement in apparatus for detecting glowing contacts in a power circuit.